This invention relates to processes designed to treat mono ethylene glycol (MEG) used in the oil and gas industry, especially in offshore locations, to control hydrates formation. More particularly, the invention relates to MEG reclamation processes which are designed to remove salts and other contaminants from a wet MEG feed stream.
In the oil and gas industry, dry (lean) MEG is used to control the formation of hydrates within the produced stream. The now wet (rich) MEG is, in turn, dried by way of a MEG reclamation process so the MEG can be used again in hydrate control.
The unit used to recover MEG usually includes three sections: pre-treatment, flash separation, and MEG regeneration. Those sections can be followed by salt management and calcium removal sections.
In the pre-treatment stage, the rich MEG containing some dissolved gas and hydrocarbon liquids must pass through a three-phase separator vessel. The gas is flashed and recovered hydrocarbon liquids are sent to the production separator. The rich MEG is sent to a flash separator. The rich MEG stream comprised of produced water and MEG is fed to the flash separator where it is brought into contact with a hot recycle stream of MEG. The flash separator operates under vacuum. The MEG and water components of the rich MEG stream are flashed and exit through the top of the flash separator where they are sent to the MEG distillation column for regeneration. The salt components of the rich MEG stream precipitate in the flash separator.
The MEG regeneration section is a refluxed distillation column. The distillation column also operates under vacuum and distills the water from the MEG-water vapors coming off the top of the flash separator. Salt-free, lean MEG produced at the bottom of the distillation column is pumped to storage for reuse. The vaporized water passes overhead from the distillation column. The water is condensed and collected in the reflux drum. A small amount is returned to the distillation column as reflux, and the remaining is routed to treatment.
The salt crystals that precipitate in the flash separator are separated by gravity to the bottom of the brine column, where they are transferred to the salt tank. There, the salts are concentrated before removal through a centrifuge.
The salts in produced water cover a variety of species, but generally are categorized into monovalent salts (typically sodium and potassium), and divalent salts (typically calcium and magnesium). The divalent salts cannot be effectively precipitated in the same manner as the monovalent salts, so a separate calcium removal process may be installed. Effective calcium control is accomplished as the divalent salts are collected, reacted and removed through a centrifuge with the centrate overflow returning to the process.
Current methods of removing the salt crystals from bottom of the brine column involves a lot of equipment, including but not limited to complicated and expensive centrifugal filters or desanding cyclones, centrifuge pump filtration systems, a salt tank, a centrate tank, and a density measurement device. Reducing the footprint of the system required to remove the salt crystals is important for making more efficient use of space, reducing off-shore construction costs, and increasing ease of system operation and maintenance.